Last updated: August 18, 2012
A burl is a rounded growth on the trunk or branch of a tree. This specialized deformity is a result of stress and abnormal growth in the grain of wood. Injury, virus and fungus can all cause burls. They are usually covered in bark and do not hurt the tree unless the weight of the tree causes breakage. Many trees have a burl underground and the burl remains undiscovered until the tree is uprooted.